A storage apparatus, such as a Redundant Arrays of Inexpensive Disks (RAID) apparatus, includes for example a channel adapter (CA) as a communication interface connected to a host computer. The CA is connected to a host bus adapter (HBA) of the host computer via, for example, a channel switch. The host computer communicates with the CA by the HBA to gain access to data stored in the storage apparatus. The CA of the storage apparatus may be used for not only communication with the host computer but also communication with another storage apparatus. For example, a flexible data replication mechanism for replicating data between storage cells has been proposed.
U.S. Patent Application Publication No. 2003/0187945
However, in the case where a single CA is used for both types of access operations, i.e., access operations made by the host computer to the storage apparatus and access operations performed with another storage apparatus, if access operations of one type increase in number, access operations of the other type are slowed. For example, it is sometimes the case that data written to a storage apparatus by a host computer is copied to a different storage apparatus in order to improve the reliability of the data. In this case, if many access operations are made by the host computer to the copy destination storage apparatus, copy processes between the storage apparatuses are suspended. Subsequently, completion of a write command issued from the host computer to the copy source storage apparatus is also delayed, which reduces the overall performance of the system. Thus, in the case of using a single communication interface of a storage apparatus for multiple purposes, an increase in data access in one use application may reduce data access efficiency in another use application. If a reduction in the data access efficiency due to such a dependency relationship takes place randomly, the overall processing efficiency of the system decreases.